During sexual reproduction in toads, the male grasps the female from behind and fertilizes the eggs as they are deposited.
Some aquatic animals also use internal fertilization.
The male may deposit sperm in the female during sex.
It may happen when a female picks up sperm in the environment and deposits it in her reproductive tract.
There are three ways in which offspring are produced.
This occurs in a number of animals and birds.
Eggs produced by birds and turtles have high concentrations of calcium carbonate in the shell, making them hard.
Chicken eggs have a hard shell.
The platypus and echidna have leathery eggs.
Eggs are kept in the female's body until they hatch inside of her, or she lays them before they hatch.
Eggs are protected until they hatch.
They get their sustenance from the female and are born in different states of maturity.
Nutrition is supported by the placenta in mammals, as was the case with this (c) newborn squirrel.
The process by which a single-celled zygote becomes a multi-cellular one is complex and well regulated.
The regulation occurs through signaling between cells and tissues.
To ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must be fused with an egg.
The acrosome is at the tip of the sperm cell's head.
A series of events take place when a sperm binding to the zona pellucida.
The sperm nucleus can be transferred into the ovum through the use of these reactions.
A diploid nucleus or genome is formed when the egg and sperm's nuclear membranes break down.
Sperm and egg form a zygote when they are fertilized.
To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg, the egg releases proteins in other locations to prevent other sperm from fusing with the egg.
The embryo will be formed by the inner cell mass.
The blastocyst can be deposited into the endometrium of the uterus with the help of the trophoblast.